No abstract

Flow in the wake of a blunt trailing edge profiled body, comprised of an elliptical leading edge and a rectangular trailing edge, has been investigated experimentally, to identify and characterize the secondary instabilities accompanying the von Kármán vortices. The experiments, which involve laser-induced fluorescence for visualization and particle image velocimetry for quantitative measurement of the wake instabilities, cover Reynolds numbers ranging from 250 to 2,150 based on thickness of the body, to include the wake transition regime. The dominant secondary instability appears as spanwise undulations in von Kármán vortices, which evolve into pairs of counterrotating vortices, with features resembling the instability mechanism predicted by Ryan et al. (J Fluid Mech 538:1-29, 2005). Feasibility of a flow control approach based on interaction with the secondary instability using a series of discrete trailing edge injectors has also been investigated. The control approach mitigates the adverse effects of vortex shedding in certain conditions, where it is able to amplify the secondary instability effectively.

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Large Eddy Simulations are carried out to analyze flow past flat plate in different configurations and inclinations. A thin flat plate is considered at three inclination angles (α = 30°, 60° and 90°) and three aspect ratios (AR = 0.5, 2 and 5). The Reynolds number based on the free stream velocity and chord length of the plate at different inclination angles varies between 75,000 to 150,000. An increase in the inclination angle while the aspect ratio (span to chord) is constant results in higher drag and lower lift on the plate. Increasing the aspect ratio at a constant inclination angle increases the mean aerodynamic loading except for the α = 30° and AR = 0.5 case where the mean forces are larger than the other aspect ratios for this specific inclination angle. The small aspect ratio suppresses and blocks the separation of the flow from the top and bottom edges causing larger aerodynamic forces relative to AR = 2, 5. Visualization of the flow structures shows the tip vortices have a significant role in controlling the shedding vortices from the top and bottom edges. At α = 30° and AR = 0.5, the two tip vortcies control and suppress the flow separation from the top and bottom edges. A stable wake was found for this case with no fluctuation. As the aspect ratio increases, the influence of the tip vortices on flow separation from the top and bottom edges reduces. As a result, larger fluctuations were found for cases with higher aspect ratios.

Deposited in DRO: HT y™to˜er PHIT Version of attached le: €u˜lished †ersion Peer-review status of attached le: €eerEreviewed Citation for published item: q—nD vF —nd urogst—dD €FE ¦ eF @PHITA 9ivolution of tur˜ulen™e —nd inEpl—ne vorti™es in the ne—r (eld)ow ˜ehind multiEs™—le pl—n—r gridsF9D €hysi™s of)uidsFD PV @VAF HVSIHIF Further information on publisher's website: httpXGGdxFdoiForgGIHFIHTQGIFRWTHHPS Publisher's copyright statement: ™ PHIT emeri™—n snstitute of €hysi™sF „his —rti™le m—y ˜e downlo—ded for person—l use onlyF eny other use requires prior permission of the —uthor —nd the emeri™—n snstitute of €hysi™sF „he following —rti™le —ppe—red in q—nD vF urogst—dD €FE ¦ eF @PHITAF ivolution of tur˜ulen™e —nd inEpl—ne vorti™es in the ne—r (eld)ow ˜ehind multiEs™—le pl—n—r gridsF €hysi™s of pluids PV@VAX HVSIHI —nd m—y ˜e found —t httpXGGdxFdoiForgGIHFIHTQGIFRWTHHPS Additional information: Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full DRO policy for further details. In this experimental work, we carry out detailed two-dimensional particle image velocimetry investigations for the near field wakes behind a conventional and two multi-scale planar grids, using stitched camera fields of view. Statistical independent measurements are conducted focusing on the first few mesh distances downstream of the grid. It is found that the multiple integral length scales originated from the grids loose their importance on the turbulence development after about three mesh distances downstream, much earlier than the distance where the turbulence becomes homogeneous. The largest eddy size, represented by the integral length scales, does not show clear differences in its growth rate among the three grids after an initial development of three times the largest grid size downstream. Nevertheless, when examining individual vortex behaviours using conditional averaging and filtering processes , clear differences are found. The grids are found to have different decay rates of peak vorticity and projected vortex strengths. Despite these differences, the in-plane vorticity correlation function reveals that the mean vortex shape of all the grids shows a universal near-Gaussian pattern which does not change much as the turbulence decays. Published by AIP Publishing. [http://dx.